One area of recent advancement is the development of different memory types, each with different characteristics. An important aspect of a majority of electronic devices is the ability to store information in digital memory, which stores information as a series of I/Os. Digital memory is a broad category with many different types of subset memory. One memory type is read-only memory (ROM). ROM is a non-volatile memory type that a system can write to only once. Non-volatile memory can retain information without a constant source of power. The system can read the information stored in the memory, but it cannot re-write new information to the memory. Oftentimes, memory writing takes place during the manufacturing process, thus many times a consumer never writes to ROM memory.
One of the most common and important types of memory in an electronic device is random access memory (RAM), which is memory that allows information to be read in any order regardless of its stored sequence. RAM is the main working area for most computer systems, such as personal computers. Electronic devices can read the information stored in RAM and they can write new information to RAM. One major flaw with RAM is that most types are volatile memory types, meaning that they need to draw from a constant source of power to retain their memory.
The most common form of RAM is dynamic random access memory (DRAM). In an integrated circuit, each bit of data is stored in an individual capacitor as an I/O. The capacitors lose voltage due to natural leakage and stored data is lost unless the system recharges the capacitor. The addition of the term dynamic is because a constant activity is taking place (e.g., the constant recharging of a capacitor). There are several variations on DRAM, such a video DRAM. There are other types of RAM, such as static random access memory, but they are less common then DRAM.
Other memory types exist to alleviate the problems present in ROM and RAM. One of the basic memory types created for alleviating these flaws is Electrically Erasable Programmable Read Only Memory (EEPROM), which is both non-volatile and capable of multiple writes and reads. However, EEPROM is rather expensive to manufacture, thus making it impractical for most personal applications. Flash memory technology is an alternative to EEPROM. In addition to being readable, re-writable (e.g., erased and written to again), and non-volatile, flash memory is relatively cheap to mass-produce. The economic factor makes flash memory much more appropriate for personal applications, such as storing of digital photographs and storing digital music files. Flash memory devices generally have a guaranteed life span of about one million programming cycles. Information in flash memory devices is stored on wordlines and bitline. To erase the information, a voltage is applied that erases stored information.